Skeletal muscle metastasis in a patient with Wilms tumor and multiple late recurrences

Stage III Wilms tumor was diagnosed in a 9-year-old girl. Four and a half years after the treatment, which consisted of an operation, radiation therapy, and chemotherapy, the patient had a solitary metastasis in the liver, which was successfully treated with chemotherapy and surgical resection. Five years later, right lung metastases were eradicated by chemotherapy, radiation, and surgical resection. Three and a half years later, she had a metastasis in the left calf, for which she underwent surgical resection and received chemotherapy. This patient has several interesting features: (1) multiple recurrences, two in the usual sites of metastasis and one in an extremely rare site, i.e., skeletal muscle; (2) long intervals between recurrences; and (3) unusual histopathologic features, i.e., gradual evolution from a triphasic Wilms tumor at the primary site, to a predominance of differentiated mucinous epithelium in the skeletal muscle metastasis.